|  | 5.1 | The Network Layer Basics
| 5.1.4 | Metrics

It is important that a routing table be up-to-date and accurate, because its primary purpose is to provide the best information for the router. Each routing protocol interprets the "best path" in its own way. The protocol generates a value called a metric, for each path through the network. Typically, the smaller the metric, the better the path. Routing tables can also contain information about the desirability of a path. Routers compare metrics to determine the best routes. Metrics differ depending on the design of the routing protocol being used. A variety of common metrics are described later in this chapter. A variety of metrics can be used to define the best path. Some routing protocols, such as Routing Information Protocol (RIP), use only one metric, and some routing protocols, such as IGRP, use a combination of metrics. The metrics most commonly used by routers are shown in the table in Figure .
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